1. Technical Field
The present invention relates to an introducer apparatus for a medical device, and more particularly, to an introducer apparatus for use in the delivery of a self-expandable medical device, such as a radially self-expandable intraluminal stent.
2. Background Information
The term “stent” is generally used in the medical field to describe a device that is inserted into a vessel or passageway to reinforce, support, repair or otherwise enhance the performance of the lumen of the vessel or passageway. For instance, in cardiovascular surgery it is often desirable to place a stent in the coronary artery at a location where the artery is damaged or susceptible to collapse. The stent, once in place, reinforces that portion of the artery, thereby allowing normal blood flow to occur through the artery.
One form of stent which is particularly desirable for implantation in arteries and other body lumens is a cylindrical stent which is radially expandable upon implantation from a smaller first diameter to a larger second diameter. Such radially expandable stents can be inserted into the artery by being positioned on a catheter in a compressed state and fed internally through the arterial pathways of the patient until the stent is located at the desired site. Radially expandable stents are normally of one of two general types. One such type is generally referred to as a “pressure-expandable” stent. With this type of stent, a catheter is fitted at its distal portion with a balloon or other expansion mechanism. The expansion mechanism exerts a radial pressure outward on the compressed stent, thereby causing the stent to expand in the radial direction to a larger diameter. Such expandable stents exhibit sufficient radial rigidity after being expanded that they will remain in the expanded condition after the expansion mechanism and catheter have been removed. The other type is generally referred to as a “self-expandable” stent. This type of stent is generally formed from a resilient or shape memory material which is capable of self-expanding from a compressed condition to an expanded condition without the application of an outwardly-exerted force on the stent. Typically, self-expansion occurs upon the removal of a restraining device, such as a sheath, that holds the stent in a compressed condition.
Although each type of stent listed above has its advantages, certain disadvantages also persist with each type. For example, with a pressure-expandable stent, a balloon or other expandable mechanism must be provided that is capable of exerting the requisite outwardly-directed pressure. This entails the incorporation of additional structure and complexity, and therefore additional expense, to a stent introducer mechanism than would otherwise be required. Self-expandable stents generally require the inclusion of an outer sheath or like structure to hold the stent in its compressed condition, and a delivery mechanism to force the stent out of the sheath at the site of expansion. The addition of an outer sheath adds bulk to the introducer apparatus, and increases its diameter. Any increase in the diameter of the introducer apparatus is inherently undesirable because it limits the size of the body vessel into which the apparatus can be introduced.
It is desired to provide an introducer apparatus for a self-expandable stent or other insertable medical device that avoids the problems of prior art introducers. More particularly, it is desired to provide an introducer apparatus that does not require the incorporation of a balloon or other expandable mechanism to exert radial pressure on the stent, and does not require the use of an outer sheath and/or related structure to restrain the stent in its compressed condition.